Installation of various type metal structures in corrosive liquids such as sea water are confronted with a major problem in avoiding the adverse effects of corrosion and erosion. Either can severely reduce the life expectancy of the structure. Exemplifying the situation are structures such as off-shore rigs for recovering oil in the many oceans and seas of the world. Briefly such structures include not only supports for the rig itself, but also risers comprising conduits through which recovered oil is transmitted. Typically, the various structural items and/or risers are pre-coated, encased or otherwise provided with cathodic protection or the like in order to ward off or deter the deleterious corrosive effects of the sea water. Little has been known however, how to restore such risers on site after the onset of corrosion when the original protective coating, etc., has begun to wear or generally deteriorate. Temporary repair or replacing the affected structures has been customary although undesirable because of the associated high costs and less than satisfactory results.